Exploring hydrogen: looking at H-alpha light
H-alpha is a deep red wavelength of light emitted by hydrogen, the most common element in the Universe and a vital building block of stars and emissive nebulae (clouds of gas and dust that emit their own light).
Dr Ed Bloomer explains, “Different physical processes produce light at different wavelengths, so different filters can be used to create images revealing those activities, or the elements producing that light.”
Weitang says, “Although we already had the LRGB data, we also wanted to highlight the H-alpha structures in this region.”
He continues, “We tried several times to collect H-alpha data to reveal the rich details in the arms. At that time, the core did not attract my attention because of relatively lower resolution. But now, with a telescope capable of achieving the best detail, we decided to revisit the core – and finally obtained 23 hours of H-alpha data.”
The photographers explain why they did this: “By carefully isolating and processing the H-alpha channel, we were able to enhance the visibility of these ionised gas clouds, which trace ongoing star formation.
“The contrast between these glowing regions and the surrounding dust lanes adds depth and dimension, offering a fresh perspective on this familiar galaxy.”
Picking a colour palette
Weitang explains the bold red colour palette: “The H-alpha spiral arms in the core were the most important feature we wanted to highlight, so we chose a striking colour that would stand out from the star field. At the same time, we also wanted to preserve the natural beauty of the star field.”
“We presented the spiral H-alpha arms in a reddish tone, finally choosing a palette where the red includes hints of orange.”
Dr Bloomer says: “The colouring is interesting. It’s not the usual colour palette, and the dominant red is powerful, but we [the judges] thought it was not uncomfortably so.”
The final image fulfilled all of the team’s expectations, and more. Weitang recalls: “At first, we were overwhelmed with excitement. Later, we calmed down and set the image aside for a few weeks. When we revisited the image after some time, we were still fully satisfied with the result. That’s when we knew it was ready to share.”
Why was this image selected as the winner?
As for why this image was worthy of the top prize in the ZWO Astronomy Photographer of the Year 2025 competition, Dr Bloomer says, “We [the judges] were struck immediately by the technical achievement of retaining so much detail so close to the core, so we knew it was worth some careful consideration.
“We chatted quite a bit about the framing: it’s quite a close crop into the centre, but we also adored that the image had such a dramatic diagonal structure.”
Dr Bloomer says each judge had their own reasons for picking the image as the winner.
“To my mind, it’s a really striking image from afar but also contains enough detail to stand up to close scrutiny. In short, it took a lot of skill to capture the data at all, and good judgement to present it in such a cool way!”
When the photographers found out they had won the top prize, Weitang says, “The excitement was beyond words! We are truly grateful to the ZWO Astronomy Photography of the Year competition. It brings us great joy to share the beauty of the Universe with everyone.”